The Effects of Asymmetric Dark Matter on Stellar Evolution I: Spin-Dependent Scattering

Abstract

Most of the dark matter (DM) search over the last few decades has focused on WIMPs, but the viable parameter space is quickly shrinking. Asymmetric Dark Matter (ADM) is a WIMP-like DM candidate with slightly smaller masses and no present day annihilation, meaning that stars can capture and build up large quantities. The captured ADM can transport energy through a significant volume of the star. We investigate the effects of spin-dependent ADM energy transport on stellar structure and evolution in stars with $0.9 \leq M_{\star}/\mathrm{M}_{\odot} \leq 5.0$ in varying DM environments. We wrote a MESA module that calculates the capture of DM and the subsequent energy transport within the star. We fix the DM mass to 5 GeV and the cross section to $10^{-37} \mathrm{cm{^2}}$, and study varying environments by scaling the DM capture rate. For stars with radiative cores ($M_{\star} \lesssim 1.3\ \mathrm{M}_{\odot}$), the presence of ADM flattens the temperature and burning profiles in the core and increases MS ($X_c > 10^{-3}$) lifetimes by up to $\sim 20\%$. We find that strict requirements on energy conservation are crucial to the simulation of ADM's effects on these stars. In higher-mass stars, ADM energy transport shuts off core convection, limiting available fuel and shortening MS lifetimes by up to $\sim 40\%$. This may translate to changes in the luminosity and effective temperature of the MS turnoff in population isochrones. The tip of the red giant branch may occur at lower luminosities. The effects are largest in DM environments with high densities and/or low velocity dispersions, making dwarf and early forming galaxies most likely to display the effects.